Canine gastric surface epithelial cell function will be studied in organ culture. Cell turnover, migration, and mucus production and release will be assessed under a variety of conditions which lead to erosive gastritis. The cytoprotective effects of blood flow will be further investigated. The role of prostaglandins in Na ion transport from gastric secretory epithelium will be studied in the exteriorized chambered segment preparation. We will attempt to determine whether the enhanced sodium efflux that occurs in the presence of this agent is protective against aspirin injury.